689 research outputs found
Complexification of Gauge Theories
For the case of a first-class constrained system with an equivariant momentum
map, we study the conditions under which the double process of reducing to the
constraint surface and dividing out by the group of gauge transformations
is equivalent to the single process of dividing out the initial phase space by
the complexification of . For the particular case of a phase space
action that is the lift of a configuration space action, conditions are found
under which, in finite dimensions, the physical phase space of a gauge system
with first-class constraints is diffeomorphic to a manifold imbedded in the
physical configuration space of the complexified gauge system. Similar
conditions are shown to hold in the infinite-dimensional example of Yang-Mills
theories. As a physical application we discuss the adequateness of using
holomorphic Wilson loop variables as (generalized) global coordinates on the
physical phase space of Yang-Mills theory.Comment: 25pp., LaTeX, Syracuse SU-GP-93/6-2, Lisbon DF/IST 6.9
Recommended from our members
Fish passage hydrodynamics New Zealand context
New Zealand is home to 57 native freshwater fish species, of which a considerable number are diadromous, having to move between freshwater and saltwater at least once during their lifecycle. The economic utilisation of New Zealand rivers has largely been carried out without fish migration behaviour in mind, resulting in thousands of structures that prevent fish migration up- and downriver. Remediation of existing structures, especially culverts, and construction of new, more fish friendly, structures requires in-depth knowledge of the needs of the target fish species. In April 2018, the New Zealand Fish Passage Guidelines were released, providing a design framework to enable fish passage in new and existing structures. In support of the new guidance, our project aims to gain insight into the swimming behaviour and performance of inanga (Galaxias maculatus) under various hydraulic conditions, in particular when swimming upstream, which is not well understood. For this purpose, we are designing a new experimental setup in a 600 mm wide flume at the Water Engineering Laboratory at the University of Auckland. We will study hydrodynamics of fish passes with roughened surfaces, baffles and energy dissipators. We will evaluate sensor equipment used to enable flow and fish tracking, with the intention of tracking individual inanga at critical cross sections. This will allow us to study fish response to turbulence, boundary layers, resting zones and wetted margins. We aim to gain valuable insight into design methods and materials that best help inanga, and potentially other members of the family Galaxiidae, with their migration. Eventually, the project aims to provide guidelines suitable for retrofitting existing and building new structures
The High Magnetic Field Phase Diagram of a Quasi-One Dimensional Metal
We present a unique high magnetic field phase of the quasi-one dimensional
organic conductor (TMTSF)ClO. This phase, termed "Q-ClO", is
obtained by rapid thermal quenching to avoid ordering of the ClO anion. The
magnetic field dependent phase of Q-ClO is distinctly different from that
in the extensively studied annealed material. Q-ClO exhibits a spin density
wave (SDW) transition at 5 K which is strongly magnetic field
dependent. This dependence is well described by the theoretical treatment of
Bjelis and Maki. We show that Q-ClO provides a new B-T phase diagram in the
hierarchy of low-dimensional organic metals (one-dimensional towards
two-dimensional), and describe the temperature dependence of the of the quantum
oscillations observed in the SDW phase.Comment: 10 pages, 4 figures, preprin
On two superintegrable nonlinear oscillators in N dimensions
We consider the classical superintegrable Hamiltonian system given by
, where U
is known to be the "intrinsic" oscillator potential on the Darboux spaces of
nonconstant curvature determined by the kinetic energy term T and parametrized
by {\lambda}. We show that H is Stackel equivalent to the free Euclidean
motion, a fact that directly provides a curved Fradkin tensor of constants of
motion for H. Furthermore, we analyze in terms of {\lambda} the three different
underlying manifolds whose geodesic motion is provided by T. As a consequence,
we find that H comprises three different nonlinear physical models that, by
constructing their radial effective potentials, are shown to be two different
nonlinear oscillators and an infinite barrier potential. The quantization of
these two oscillators and its connection with spherical confinement models is
briefly discussed.Comment: 11 pages; based on the contribution to the Manolo Gadella Fest-60
years-in-pucelandia, "Recent advances in time-asymmetric quantum mechanics,
quantization and related topics" hold in Valladolid (Spain), 14-16th july
201
Clinical and laboratory variability in a cohort of patients diagnosed with type 1 VWD in the United States
Von Willebrand disease (VWD) is the most common inherited bleeding disorder, and type 1
VWD is the most common VWD variant. Despite its frequency, diagnosis of type 1 VWD
remains the subject of much debate. In order to study the spectrum of type 1 VWD in the United
States, the Zimmerman Program enrolled 482 subjects with a previous diagnosis of type 1 VWD
without stringent laboratory diagnostic criteria. VWF laboratory testing and full length VWF
gene sequencing were performed for all index cases and healthy control subjects in a central
laboratory. Bleeding phenotype was characterized using the ISTH Bleeding Assessment Tool.
At study entry, 64% of subjects had VWF:Ag or VWF:RCo below the lower limit of normal,
while 36% had normal VWF levels. VWF sequence variations were most frequent in subjects
with VWF:Ag < 30 IU/dL (82%) while subjects with type 1 VWD and VWF:Ag ≥ 30 IU/dL had
an intermediate frequency of variants (44%). Subjects whose VWF testing was normal at study
entry had a similar rate of sequence variations as the healthy controls at 14% of subjects. All
subjects with severe type 1 VWD and VWF:Ag ≤ 5 IU/dL had an abnormal bleeding score, but
otherwise bleeding score did not correlate with VWF:Ag level. Subjects with a historical
diagnosis of type 1 VWD had similar rates of abnormal bleeding scores compared to subjects
with low VWF levels at study entry. Type 1 VWD in the United States is highly variable, and
bleeding symptoms are frequent in this population
Commitments for Ethically Responsible Sourcing, Use, and Reuse of Patient Data in the Digital Age: Cocreation Process
Background: Personal information, including health-related data, may be used in ways we did not intend when it was originally shared. However, the organizations that collect these data do not always have the necessary social license to use and share it. Although some technology companies have published principles on the ethical use of artificial intelligence, the foundational issue of what is and is not acceptable to do with data, not just the analytical tools to manage it, has not been fully considered. Furthermore, it is unclear whether input from the public or patients has been included. In 2017, the leadership at a web-based patient research network began to envision a new kind of community compact that laid out what the company believed, how the company should behave, and what it promised both to the individuals who engaged with them and to the community at large. While having already earned a social license from patient members as a trusted data steward with strong privacy, transparency, and openness policies, the company sought to protect and strengthen that social license by creating a socially and ethically responsible data contract. Going beyond regulatory and legislative requirements, this contract considered the ethical use of multiomics and phenotypic data in addition to patient-reported and generated data. Objective: A multistakeholder working group sought to develop easy-to-understand commitments that established expectations for data stewardship, governance, and accountability from those who seek to collect, use, and share personal data. The working group cocreated a framework that was radically patient-first in its thinking and collaborative in the process of its codevelopment; it reflected the values, ideas, opinions, and perspectives of the cocreators, inclusive of patients and the public. Methods: Leveraging the conceptual frameworks of cocreation and participatory action research, a mixed methods approach was used that included a landscape analysis, listening sessions, and a 12-question survey. The methodological approaches used by the working group were guided by the combined principles of biomedical ethics and social license and shaped through a collaborative and reflective process with similarities to reflective equilibrium, a method well known in ethics. Results: Commitments for the Digital Age are the output of this work. The six commitments in order of priority are (1) continuous and shared learning; (2) respect and empower individual choice; (3) informed and understood consent; (4) people-first governance; (5) open communication and accountable conduct; and (6) inclusivity, diversity, and equity. Conclusions: These 6 commitments—and the development process itself—have broad applicability as models for (1) other organizations that rely on digitized data sources from individuals and (2) patients who seek to strengthen operational policies for the ethical and responsible collection, use, and reuse of that data
Geometric Approach to Pontryagin's Maximum Principle
Since the second half of the 20th century, Pontryagin's Maximum Principle has
been widely discussed and used as a method to solve optimal control problems in
medicine, robotics, finance, engineering, astronomy. Here, we focus on the
proof and on the understanding of this Principle, using as much geometric ideas
and geometric tools as possible. This approach provides a better and clearer
understanding of the Principle and, in particular, of the role of the abnormal
extremals. These extremals are interesting because they do not depend on the
cost function, but only on the control system. Moreover, they were discarded as
solutions until the nineties, when examples of strict abnormal optimal curves
were found. In order to give a detailed exposition of the proof, the paper is
mostly self\textendash{}contained, which forces us to consider different areas
in mathematics such as algebra, analysis, geometry.Comment: Final version. Minors changes have been made. 56 page
Hopf algebras and Markov chains: Two examples and a theory
The operation of squaring (coproduct followed by product) in a combinatorial
Hopf algebra is shown to induce a Markov chain in natural bases. Chains
constructed in this way include widely studied methods of card shuffling, a
natural "rock-breaking" process, and Markov chains on simplicial complexes.
Many of these chains can be explictly diagonalized using the primitive elements
of the algebra and the combinatorics of the free Lie algebra. For card
shuffling, this gives an explicit description of the eigenvectors. For
rock-breaking, an explicit description of the quasi-stationary distribution and
sharp rates to absorption follow.Comment: 51 pages, 17 figures. (Typographical errors corrected. Further fixes
will only appear on the version on Amy Pang's website, the arXiv version will
not be updated.
Mitotic phosphorylation by NEK6 and NEK7 reduces microtubule affinity of EML4 to promote chromosome congression
EML4 is a microtubule-associated protein that promotes microtubule stability. We investigated
its regulation across the cell cycle and found that EML4 was distributed as punctate foci along
the microtubule lattice in interphase but exhibited reduced association with spindle
microtubules in mitosis. Microtubule sedimentation and cryo-electron microscopy with 3D
reconstruction revealed that the basic N-terminal domain of EML4 mediated its binding to the
acidic C-terminal tails of α- and β-tubulin on the microtubule surface. The mitotic kinases
NEK6 and NEK7 phosphorylated the EML4 N-terminal domain at Ser144 and Ser146 in vitro,
and depletion of these kinases in cells led to increased EML4 binding to microtubules in
mitosis. An S144A-S146A double mutant not only bound inappropriately to mitotic
microtubules but also increased their stability and interfered with chromosome congression.
Meanwhile, constitutive activation of NEK6 or NEK7 reduced EML4 association with
interphase microtubules. Together, these data support a model in which NEK6- and NEK7-
dependent phosphorylation promotes dissociation of EML4 from microtubules in mitosis in a
manner that is required for efficient chromosome congression
Cofactorization on Graphics Processing Units
We show how the cofactorization step, a compute-intensive part of the relation collection phase of the number field sieve (NFS), can be farmed out to a graphics processing unit. Our implementation on a GTX 580 GPU, which is integrated with a state-of-the-art NFS implementation, can serve as a cryptanalytic co-processor for several Intel i7-3770K quad-core CPUs simultaneously. This allows those processors to focus on the memory-intensive sieving and results in more useful NFS-relations found in less time
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